The present invention relates to an elastomer-made push button switch covering member or, more particularly, to an elastomer-made push button switch covering member composed of a base portion, a top portion and a riser portion connecting the base portion and the top portion into a dome-like configuration, of which the switching stroke does not exceed 0.5 mm and the click ratio is at least 30% to ensure high efficiency of switching operation with very reliable and pleasant feeling of touch on the operator's finger tip.
In recent years, flat-panel key board switches are widely used, for example, in various kinds of input switches including remote control switching units. In view of the usually very small switching stroke in such flat-panel keyboard switches, it is essential that the switching operation of the switch can be definitely recognized by pushing the switch with a finger tip. Such a recognition can be obtained in several different ways including light and sound signals although the most preferable and reliable way is practically that the pushing finger tip receives a clearly recognizable feeling of clicking touch from the key top.
Push button switch covering members are sometimes made of a relatively rigid material with an object to prevent deformation and slackening after use for a prolonged period of time so that the switching stroke of a key board switch having such a covering member can rarely be larger than 0.2 to 0.5 mm. When the switching stroke is so small, conventional rubber-made push buttom switches can hardly give the pushing finger tip a definite and reliable feeling of clicking touch which is expressed by the click ratio defined by (a-d)/a.times.100 (%), in which a is the pushing load at the peak and d is the pushing load at the moment of clicking in the pushing stroke vs. pushing load diagram.
A solution for the above mentioned problem is obtained by the use of a resilient diaphragm made of a metal such as German silver, phosphor bronze, stainless steel and the like in a downwardly concave configuration as a movable contact member facing the fixed contact points therebelow and coming into contact therewith when pressed down. Such a resilient metal-made diaphragm member can give a considerably good touch of clicking with a click ratio as high as 46.7% by the reversal of the curvature at a certain point in the course of increase of the pushing load. A problem of such a push button switch is the low reliability and durability due to the fatigue of the metal-made diaphragm to fail to regain the original unpressed configuration after a clicking takes place and dust particles entering between the fixed contact point and the diaphragm to cause failure in establishing electric connection therebetween. Moreover, another disadvantage is that the productivity in the assembling works of push button switches of such a metal-made diaphragm type cannot be high enough because each push button switch must contain a metal-made diaphragm inserted between the covering member and the base board with accuracy in position to ensure centering of the pushing load relative to the diaphragm even by setting aside the problem caused by the increased number of the parts to be assembled into a push button switch.